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Ken
Ken, ASE Certified Technician
Category: GM
Satisfied Customers: 754
Experience:  GM & SATURN Factory Trained Technician, 25 Years Experience
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A 1998 gmc suburban 4x4 5.7 engine. When engine is cold, it

Customer Question

A 1998 gmc suburban 4x4 5.7 engine. When engine is cold, it starts good as usual and idles good but when you start to drive the vehicle, it sometimes will act like it is cutting out or missing under slow acceleration until it warns up and then the issue goes away. If you do a fast acceleration when it is missing, it runs great but starts missing again under slow acceleration. The vehicle is not setting any error codes which is weird. New plugs, wires and new egr valve have not helped. This is a very intermittent problem and diagnostics have not shown any problems...
Submitted: 5 years ago.
Category: GM
Expert:  Carhelp4u replied 5 years ago.
How many miles are on this vehicle? Any recent tune ups? Has any testing been done to verify fuel pressure?
Customer: replied 5 years ago.
Vehicle has 181,653 miles..   Tune was done about two weeks ago..No fuel pressure checks have been done.
Expert:  Carhelp4u replied 5 years ago.

Sorry for the delay, what items were replaced during the tune up? Do you have access to a fuel pressure tester?

Customer: replied 5 years ago.
Plugs, plug wires, Dist. Cap, filters, some coolant hoses...All Vacumn hoses were checked but none replaced...No, I don't have access to a fuel pressure tester...How would that be related to this issue?
Expert:  Carhelp4u replied 5 years ago.
Well honestly I am not saying that it is relevant, but I have seen many cases in which low fuel pressure on the vortec engine can cause for some strange problems. This fuel system is designed to operate at a 60-66 psi range. Running the fuel pressure will drop to no less than 55 psi. If you are having a fuel pressure problem in which the fuel pressure is low you could possibly see this problem. The problem going away with a quick throttle could just be due to the fact that the fuel pressure regulator is raising the pressure to an appropriate level. I would certainly feel that this would be a good test to do. Normally if this is an electronic engine control fault you would see a check engine light at some point. Not always, but most of the time. Beyond this you may really need access to a class 2 scan tool to verify that the engine control sensors are operating as they should. If you can do this testing and get back to me I would be happy to further assist you. If not, let me know and I will opt out to see if any other experts have any input.
Customer: replied 5 years ago.
If it is fuel pressure related, would that mean the fuel filter or fuel pump or maybe both?
Expert:  Carhelp4u replied 5 years ago.
I would have replaced the fuel filter during the last tune up. If not, it may be a real good place to start. If the pressure is not within the specs I listyed above, then we need to look at the fuel pump, and fuel pressure regulator for starters. This type of testing can get rather in depth as you must eliminate one or the other. There are fuel pressure testers that actually attach at the fuel filter. This can allow for you to test the fuel pump alone.
Customer: replied 5 years ago.
I had to replace the fuel pump on this vehicle about 10 months ago and the mechanic replaced the fuel filter at the same time...That's why it wasn't done during the tuneup. I thought the fuel pressure was suppose to be constant thru out all driving ranges (speeds)? Also, if fuel pressure is the villan, why does it go away after the engine warms up? Just curious!
Expert:  Carhelp4u replied 5 years ago.
Well a cold engine requires a bit more fuel than a warmed up engine. Your right the fuel pressure should be rather consistent, but yet with a quick flip of the throttle the pressure needs to rise. if the rising pressure puts you in the required range, but at idle the pressure is too low you could certainly have these problems. As I stated, this would just be a rather easy item to look at to verify this problem. There are many other items that could cause for this, but without this vehicle doing this consistently you are going to be very limited as to what you can check unless you get a check engine light. Another thing I would like to add would be an intake gasket failure. These engines used a plastic gasket with a rubber inset seal. The plastic is commonly known to crack in which can cause a vacuum leak. After the engine warms up a bit, the intake to cylinder head clearance tightens and the problem goes away. Just another thought.
Customer: replied 5 years ago.
OK, I'll see if the mechanic up the street from me can do a fuel pressure check tomorrow...If so, how do I re-connect with you as to the results?
Expert:  Carhelp4u replied 5 years ago.
You can log in and come back to this post. If the vehicle is acting up, that would be the best time to do the testing.
Customer: replied 5 years ago.
ok...will do
Expert:  Carhelp4u replied 5 years ago.
Thanks for understanding. I just would rather assist you with the proper testing rather than throwing any more parts at this vehicle.
Customer: replied 5 years ago.
Hello....I have completed a fuel pressure test. At idle, it has a constant 56 psi. under fast idle it will jump to 58 and then drop back to 56 psi. We check this with engine cold and hot. Also, when we tested it with engine cold, it did the missing/cutting out act but the psi remained constant at 56psi.
Expert:  Ken replied 5 years ago.
Hi and thanks for your question! Checking the injectors would be my next step. The injectors are known on this more for sticking cold. Ken
#00-06-04-003B: Rough Idle After Start, And/Or A Service Engine Soon (SES) Light (Unstick And Clean Central Sequential Fuel Injection (CSFI) Poppet Valves or Convert to MFI) - (Jan 30, 2003)

Subject:Rough Idle After Start, And/Or A Service Engine Soon (SES) Light (Unstick And Clean Central Sequential Fuel Injection (CSFI) Poppet Valves or Convert to MFI)

Models:1995-2002 Chevrolet and GMC S/T Models
1996-2002 Chevrolet and GMC C/K, M/L, G, P Models
1996-2001 Oldsmobile Bravada
1999-2000 Cadillac Escalade
with 4.3L, 5.0L or 5.7L Engine (VINs W, X, M, R -- RPOs L35, LF6, L30, L31)
Except 2002 VIN X -- RPO LU3 Models

 


 

Condition

Some customers may comment on rough idle after start-up, especially if the vehicle has sat overnight. These symptoms may be intermittent. The Service Engine Soon (SES) light may also be illuminated. Current misfire or history misfire codes may be detected with the Tech 2 scan tool.

Cause

A deposit build-up on the CSFI poppet valve ball and/or seat may cause the poppet ball to stick open or closed. In either case, the specific cylinder will be mis-fueled, resulting in a cylinder mis-fire condition.

Correction

A new injector unsticking and cleaning process has proven to be effective in restoring poppet valves to an "as new" condition. CSFI injector replacement should NOT be considered as a correction for this customer concern.

Check the vehicle history to determine if the vehicle is returning for a second fuel system repair for this condition. If the fuel system has been repaired for this condition previously, then inform the customer that an alternate fix is available. A new MFI fuel system has been developed that will back service the CSFI fuel system. The MFI fuel system eliminates the CSFI poppet valve ball and seat. The CSFI fuel system will need to be replaced as a unit. Refer to Central SFI to MFI Conversion instructions in this bulletin.

Notice: Individual CSFI injectors can not be replaced with MFI injectors. The entire CSFI fuel meter body will need to be replaced. The bracket used to retain the injectors in the fuel meter body is different between the CSFI and MFI unit. The unit may not seal if you mix injectors. Severe engine damage could result.

Cleaning the CSFI injectors is the preferred repair. The CSFI unit should not be replaced until cleaning has been attempted. If the vehicle should return for the same repair, then the CSFI unit can be replaced with an MFI unit. If the vehicle is out of warranty, the customer should be given the option of which fix to pursue.

Important: "GM of Canada" dealers require District Service Manager approval prior to replacing the CSFI unit with a MFI unit under warranty.

The first step of this process is to use the J 41413 Evap Pressure/Purge Station, in conjunction with the J 44466-10 pressure regulator/hose assembly, to provide the required high pressure (150 psi) source to perform the unsticking procedure. The J 39021 fuel injector tester and accessories provide the means to "energize" the injector. Some later model-year vehicles may utilize the Tech 2® to "energize" the injectors.

The second step of this process is to run the engine on a solution of 10% Top Engine Cleaner and 90% gasoline. This will effectively clean any deposits from the ball and seats of the poppets. It is very important that the engine fuel system is separated from the vehicle fuel system. Top Engine Cleaner may have detrimental effects on the fuel pump.

Cleaning Procedures

This procedure should be performed before any attempt to convert the fuel system to MFI.

S/T and C/K Truck

  1. Loosen the fuel filler cap to relieve vapor pressure in the fuel tank.
  2. Remove the Positive Crankcase Ventilation (PCV) clean air tube from the air inlet tube and set aside.
  3. Remove the bonnet and inlet tube from the throttle body.
  4. Remove the brake booster vacuum hose and connector from the intake manifold.
  5. Remove the electrical connector from the CSFI fuel metering body.
  6. Remove ignition wires 1, 3, 5, (7) from the distributor cap.
    Object Number: 334517  Size: SH

  7. Remove the fuel line bolt (4) at the rear of the intake manifold.
  8. Relieve the fuel system pressure at the service fitting on the fuel line. Use a shop towel to contain any fuel that may exit the service fitting.
    Object Number: 648217  Size: SH

  9. Remove the nuts (1) and clamp (2) from the fuel pipe.
  10. Remove the fuel pipes from the metering body. Be careful not to disturb the O-rings, washer, and spacer in the metering body.
    Object Number: 648221  Size: SH

  11. Install the J 44466-12 (2) and the J 44466-13 (1) to the metering body and tighten. Make sure that the fuel pipe O-rings, washer, and spacers are present and in their proper position.
    Object Number: 648219  Size: SH

  12. Install the J 44466-11 (4), clamp (2), and J 44466-13 (1) to the fuel pipe and tighten.
    Object Number: 648216  Size: SH

  13. Obtain the J 41413, close the valve (2) on the tank, and remove the regulator assembly.
  14. Install the J 44466-10 (5) to the J 41413 tank (3). The J 44466-10 regulator is preset to 150 psi.
    Object Number: 648224  Size: SH

  15. Connect the J 44466-10 hose (1) to the J 44466-12 (3).
  16. Install the J 39021 Injector/Coil Balance Tester, the J 39021-210 Injector Tester Adapter Box, and J 39021-301 V6 Fuel Injector Test Adapter (1) or J 39021-302 V8 Fuel Injector Test Adapter to the metering body electrical connector.
  17. Adjust the amperage selector switch on J 39021 to 0.5 amps.
    Object Number: 648216  Size: SH

  18. Open the valve (2) on the tank (3).
  19. Open the valve (4) on the J 44466-10 to pressurize the fuel system. The minimum pressure required on the gauge (6) is 150 psi. If 150 psi is not obtained, the tank (3) must be refilled prior to performing this procedure.
  20. Close the valve (4) on the J 44466-10.
  21. Energize one injector using the J 39021. Observe a pressure drop on the gauge (6) and verify the injector/poppet valve operation. An injector/poppet that is "stuck" and not operational will have no pressure drop on the gauge. If an injector remains "stuck", repeat the procedure multiple times (as required) until the injector is operational.
  22. Repeat steps 19, 20 and 21 for each individual injector to verify that all injector/poppet valve assemblies are "unstuck" and functional.
  23. Shut off pressure valve (2) on the tank (3) of the J 41413.
  24. Bleed off the pressure at the J 44466-10.
  25. Disconnect and remove the J 44466-10 (5) from the J 44466-12, and the J 41413.
  26. Remove the J 39021-301 or J 39021-302, J 39021-210, and J 39021 from the metering body.
  27. Install the vehicle electrical connector to the metering body.
  28. Install the brake booster vacuum hose and connector to the intake manifold.
  29. Install ignition wires 1, 3, 5, (7) to the distributor cap.
  30. Install the air inlet bonnet to the throttle body, tighten the wing-nut.
  31. Install the PCV fresh air tube to the air inlet tube.
    Object Number: 651337  Size: SH

  32. Obtain J 35800-A (2). Make sure the valve at the bottom of the canister (3) is closed.
  33. Remove the canister top and add 24 ml (0.8 fl.oz.) Top Engine Cleaner, P/N(NNN) NNN-NNNN(Canada P/N 992872), to the canister.
  34. Fill the remainder of the canister with regular unleaded gasoline and install the canister top.
  35. Suspend J 35800-A from a convenient underhood location.
  36. Connect the hose from J 35800-A to the service port on the J 44466-12.
  37. Open the valve (3) at the bottom of J 35800-A.
  38. Connect a "shop air" source to the fitting at the top of J 35800-A and adjust the regulator (1) to 75 psi.
  39. Start the vehicle. It may be necessary to re-adjust the J 35800-A pressure regulator to maintain 75 psi.
  40. Let the vehicle run at idle until the canister is empty and the vehicle stalls.
  41. Remove the shop air supply from J 35800-A.
  42. Depressurize the J 35800-A.
  43. Disconnect the J 35800-A hose from the J 44466-12.
  44. Remove the PCV clean air tube from the air inlet tube and set aside.
  45. Remove the bonnet from the throttle body, and set aside.
  46. Remove ignition wires 1, 3, 5, (7) from the distributor cap.
  47. Remove the brake booster vacuum hose and connector from the intake manifold.
  48. Bleed the residual pressure from the J 44466-12.
    Object Number: 648221  Size: SH

  49. Remove J 44466-13 (1) and J 44466-12 (2) from the metering body.
    Object Number: 648219  Size: SH

  50. Remove J 44466-13 (1), clamp (2), and J 44466-11 (4), from the fuel pipe (3).
    Object Number: 334517  Size: SH

  51. Install the fuel pipe (3) to the metering body. Make sure that all of the O-rings (6 and 8), washers (7), and spacers (5) are present and in their proper position.
  52. Install the clamp (2) and nuts (1).

    Tighten
    Tighten the nuts to 3 N·m (27 lb in).

  53. Apply threadlock, P/N 12345382, or equivalent to the threads of the fuel pipe bolt (4). Install the bolt.

    Tighten
    Tighten the fuel pipe bolt to 6 N·m (53 lb in).

  54. Install the brake booster vacuum hose and connector to the intake manifold.
  55. Install the bonnet and air inlet tube to the throttle body.
  56. Install the PCV fresh air tube to the inlet duct.
  57. Install ignition wires 1, 3, 5, (7) to the distributor cap.
  58. Add one (1) ounce of Port Fuel Injector Cleaner, P/N 12345104 (Canada P/N 10953467), to the vehicle fuel tank for each gallon of gasoline estimated to be in the tank. Instruct the customer to add the remainder of the bottle of Port Fuel Injector Cleaner to the vehicle fuel tank at the next fill-up. Further recommend that Port Fuel Injector Cleaner be added to the fuel tank every 3000 miles (4800 km) particularly if the vehicle is not started and driven every day. Inform the customer that the Port Fuel Injector Cleaner is not to be used at every fill up but may be reapplied every 3000 miles (4800 km).
  59. Tighten the fuel tank filler cap.
  60. Start the vehicle and check for fuel leaks.
  61. Using the Tech 2® scan tool, check for any stored Powertrain DTC codes. Clear codes as required.
  62. Disconnect the Tech 2® Scan tool.
  63. Advise the customer to change brands of fuel.

M/L, G Van and P Truck

  1. Loosen the fuel tank filler cap to relieve fuel tank vapor pressure.
  2. Remove the engine cover.
  3. Remove ignition wires 1, 3, 5, (7) from the distributor cap.
  4. Remove the vacuum brake booster hose and connector from the intake manifold.
    Object Number: 334517  Size: SH

  5. Remove the fuel pipe bolt (4) at the rear of the intake manifold.
  6. Relieve the fuel system pressure at the service fitting on the fuel pipe. Use a shop towel to contain any fuel that may exit the service fitting.
    Object Number: 331785  Size: SH

  7. Disconnect the fuel pipes (3) at the rear of intake manifold (1).
    Object Number: 648217  Size: SH

  8. Remove the nuts (1) and clamp (2) from the fuel pipe.
  9. Remove the fuel pipes from the metering body. Be careful not to disturb the O-rings, washer, and spacer in the metering body.
  10. Remove the electrical connector from metering body.
    Object Number: 648221  Size: SH

  11. Install J 44466-12 (2) and J 44466-13 (1) to the fuel metering body and tighten. Make sure that the fuel pipe O-rings, washer, and spacers are present and in their proper position.
    Object Number: 648222  Size: SH

  12. Install J 44466-01 (1) to the vehicle fuel lines.
    Object Number: 648216  Size: SH

  13. Obtain the J 41413, close the valve (2) on the tank, and remove the regulator assembly.
  14. Install the J 44466-10 (5) to the J 41413 tank (3). The J 44466-10 regulator is preset to 150 psi. The minimum pressure required on the gauge (6) is 150 psi. If 150 psi is not obtained, the tank must be refilled prior to performing this procedure.
  15. Connect the J 44466-10 hose to the J 44466-12.
  16. Install J 39021 Injector/Coil Balance Tester, the J 39021-210 Injector Tester Adapter Box, and J 39021-301 V6 Fuel Injector Test Adapter or J 39021-302 V8 Fuel Injector Test Adapter to metering body electrical connector.
  17. Adjust the amperage selector switch on J 39021 to 0.5 amps.
    Object Number: 648216  Size: SH

  18. Open the valve (2) on the tank (3).
  19. Open the valve (4) on the J 44466-10 to pressurize the fuel system.
  20. Close the valve (4) on the J 44466-10.
  21. Energize one injector using the J 39021. Observe a pressure drop on the gauge (6) and verify the injector/poppet valve operation. An injector/poppet that is "stuck" and not operational will have no pressure drop on the gauge. If an injector remains "stuck", repeat the procedure multiple times (as required) until the injector is operational.
  22. Repeat steps 19, 20, and 21, for each individual injector to verify that all injector/poppet valve assemblies are "unstuck" and functional.
  23. Shut off the pressure valve (2) on the tank (3) of the J 41413.
  24. Bleed off pressure at J 44466-10.
  25. Disconnect and remove the J 44466-10 hose from the J 44466-12 and the J 41413.
  26. Remove the J 39021-301 or J 39021-210, J 39021-210, and J 39021 from the metering body.
  27. Install the vehicle electrical connector to the metering body.
  28. Install ignition wires 1, 3, 5, (7) to the distributor cap.
  29. Install the vacuum brake booster hose and connector to the intake manifold.
    Object Number: 651337  Size: SH
    Click here for detailed picture of above image.
  30. Obtain J 35800-A (2). Make sure the valve (3) at the bottom of the canister is closed.
  31. Remove the canister top and add 24 ml (0.8 fl.oz.) Top Engine Cleaner, P/N(NNN) NNN-NNNN(Canada P/N 992872), to the canister.
  32. Fill the remainder of the canister with regular unleaded gasoline and install the canister top.
  33. Suspend the J 35800-A in a convenient location.
  34. Connect the hose from the J 35800-A to the service port on the J 44466-12.
  35. Open the valve (3) at the bottom of J 35800-A.
  36. Connect a "shop air" source to the fitting at the top of J 35800-A and adjust the regulator (1) to 75 psi.
  37. Start the vehicle. It may be necessary to re-adjust the J 35800-A pressure regulator to maintain 75 psi.
  38. Let the vehicle run at idle until the canister is empty and the vehicle stalls.
  39. Remove the shop air supply from J 35800-A.
  40. Depressurize the J 35800-A.
  41. Disconnect the J 35800-A hose from the J 44466-12.
  42. Remove the vacuum brake booster hose and connector from the intake manifold.
  43. Remove ignition wires 1, 3, 5, (7) from the distributor cap.
  44. Bleed the residual pressure from J 44466-12.
    Object Number: 648221  Size: SH
    Click here for detailed picture of above image.
  45. Remove the J 44466-13 (1) and J 44466-12 (2) from the metering body.
    Object Number: 648222  Size: SH
    Click here for detailed picture of above image.
  46. Remove the J 44466-01 (1) from the vehicle fuel lines.
    Object Number: 334517  Size: SH
    Click here for detailed picture of above image.
  47. Install the fuel pipe (3) to the metering body. Make sure the all of the O-rings (6 and 8), washers (7), and spacers (5) are present and in their proper position.
  48. Install the clamp (2) and nuts (1).

    Tighten
    Tighten the nuts to 3 N·m (27 lb in).


    Object Number: 331785  Size: SH
    Click here for detailed picture of above image.
  49. Inspect the O-rings at the fuel pipe-to-vehicle lines (1). Replace as necessary.

    Tighten
    Tighten the fuel line nuts to 30 N·m (22 lb ft).

  50. Apply threadlock, P/N 12345382, or equivalent to the threads of the fuel pipe bolt. Install the bolt.

    Tighten
    Tighten the fuel pipe bolt to 6 N·m (53 lb in).

  51. Install ignition wires 1, 3, 5, (7) to the distributor cap.
  52. Install the vacuum brake booster hose and connector to the intake manifold.
  53. Add one (1) ounce of Port Fuel Injector Cleaner, P/N 12345104 (Canada P/N 10953467), to the vehicle fuel tank for each gallon of gasoline estimated to be in the tank. Instruct the customer to add the remainder of the bottle of Port Fuel Injector Cleaner to the vehicle fuel tank at the next fill-up. Further recommend that Port Fuel Injector Cleaner be added to the fuel tank every 3000 miles (4800 km) particularly if the vehicle is not started and driven every day. Inform the customer that the Port Fuel Injector Cleaner is not to be used at every fill up but may be reapplied every 3000 miles (4800 km).
  54. Tighten the fuel tank filler cap.
  55. Start the engine and check for fuel leaks.
  56. Use the Tech 2® Scan Tool to check for any stored Powertrain DTC codes. Clear codes as required.
  57. Disconnect the Tech 2® Scan tool.
  58. Install the engine cover.
  59. Advise customer to change brands of fuel.

Central SFI to MFI Conversion Instructions

This procedure outlines the steps required to replace the existing Central SFI Fuel System with a new MFI (Multiport Flexible Injection) Fuel System. Be sure to use the appropriate year and model Service Manual for proper disassembly and re-assembly procedure(s).

Important: Cleaning the CSFI injectors is the preferred repair. The CSFI unit should not be replaced until cleaning has been attempted. If the vehicle should return for the same repair, then the CSFI unit can be replaced with a MFI unit. If the vehicle is out of warranty, the customer should be given the option of which fix to pursue.

V6 Engines

  1. Remove Upper Intake Manifold plenum and SFI Fuel Meter Body according to Service Manual Procedures.

    Figure 1


    Object Number: 900020  Size: SF

    (1)Cyl. #1 tube
    (2)Cyl. #2 tube
    (3)Cyl. #3 tube
    (4)Cyl. #4 tube
    (5)Cyl. #5 tube
    (6)Cyl. #6 tube
    (7)MFI Fuel Meter Body
  2. Remove the Fuel Meter Body bracket and discard. Install the new bracket as shown in Figure 1.

    Figure 2


    Object Number: 900019  Size: SH

    (1)Cyl. #1 tube
    (2)Cyl. #2 tube
    (3)Cyl. #3 tube
    (4)Cyl. #4 tube
    (5)Cyl. #5 tube
    (6)Cyl. #6 tube
    (7)MFI Fuel Meter Body
  3. Position Fuel Tubes of MFI Fuel Meter Body as shown in Figure 2. Tubes must be oriented away from the fuel pressure regulator end of the fuel meter body.

    Notice: The number 3 Fuel Tube must be positioned behind the number 1 Fuel Tube to eliminate interference with the Upper Intake Manifold plenum when installed. See Figure 2.

  4. Insert the MFI Fuel Meter Body into the Fuel Meter Body Bracket on the Lower Intake Manifold being careful not to bind the Fuel Tubes. Make sure that the number three Fuel Tube is routed in behind number 1 and 5 Fuel Tubes as shown in Figure 2. Push down firmly on the fuel meter body locking it into the bracket.

    Notice: Use caution when inserting injectors into lower intake manifold to be sure the correct injector is being placed into the correct hole.

    Injectors should not be removed once they have been installed.

     

     

    Removal of injectors from the intake manifold may cause damage to the retaining lugs on the injector.

     

     

    Important: The Injector holes are numbered on the Lower Intake Manifold. The injectors are numbered on the side of the Fuel Meter Body.

  5. Insert the number 3 injector into the correct Injector hole in the Lower Intake Manifold first. Install the number 5 injector next and then number 1. This sequence must be followed correctly to prevent interference of the Fuel Tubes. Injectors 2, 4, and 6 are then installed.
  6. Insure that the electrical connectors of the injectors are positioned so that they do not interfere with each other and are pointing towards the center of the Intake Manifold. If necessary, rotate the electrical connectors inboard.

    Notice: Lack of lubrication will make installation of the Upper Intake Manifold plenum difficult and may cause damage to the O-ring.

  7. Lubricate the Fuel Meter Body Upper Manifold O-ring (orange in color) with clean engine oil.
  8. Inspect the Upper Intake Manifold plenum gasket and replace if necessary. Reinstall the Upper Intake Manifold plenum following the procedures outlined in the Service Manual.

    Important: Lubricate the Fuel Inlet and Return Lines with clean engine oil before inserting them into the Fuel Meter Body.

    Make sure that the Fuel Line Retaining Bracket is properly oriented with the tabs down.

     

     

    1. Remove Upper Intake Manifold plenum and SFI Fuel Meter Body according to Service Manual Procedures.
    2. Remove the Fuel Meter Body bracket and discard. Install the new bracket.

      Figure 3


      Object Number: 900021  Size: SF

      (1)Cyl. 2, 4, 6 and 8 tubes
      (2)Fuel Inlet
      (3)Cyl. 1, 3, 5 and 7 tubes
      (4)Fuel Pressure Regulator
    3. Position Fuel Tubes of MFI Fuel Meter Body as shown in Figure 3. Fuel tubes 1, 3, 5, and 7 are oriented toward the fuel inlet side of the fuel meter body. Fuel tubes 2,4,6, and 8 are oriented toward the fuel pressure regulator side if the fuel meter body.
    4. Insert the MFI Fuel Meter Body into the Fuel Meter Body Bracket on the Lower Intake Manifold being careful not to bind the Fuel Tubes. Push down firmly on the fuel meter body until the tabs snap into the bracket locking the fuel meter body in place.
      Object Number: 900022  Size: MH

      (1)Cylinders 6 & 8
      (2)Fuel Pressure Regulator
      (3)Cylinders 2 & 4
      (4)Cylinders 5 & 7
      (5)Cylinders 1 & 3
    5. Orient the fuel tubes to coincide with their corresponding cylinder. The fuel tubes are numbered on the side of the fuel meter body and the corresponding cylinder number is XXXXX in the intake manifold.

      Notice: Use caution when inserting injectors into lower intake manifold to be sure the correct injector is being placed into the correct hole.

      Injectors should not be removed once they have been installed.

       

       

      Removal of injectors from the intake manifold may cause damage to the retaining lugs on the injector.

       

       

      Important: The Injector holes are numbered on the Lower Intake Manifold. The injectors are numbered on the side of the Fuel Meter Body.

    6. Insert the fuel tubes into their corresponding holes in the intake manifold. Install tubes for cylinders 1, 3, 6 and 8 making sure that the injector electrical connectors are facing in toward the center of the manifold.
    7. Insert fuel tubes for cylinders 2,4,5, and 7 in the same manner.

      Important: When installing fuel tubes, it is important that the tubes are oriented properly to provide minimal interference when installing the upper intake manifold plenum. Intake holes for cylinders 2, 4, 5, and 7 are closer to the fuel meter body. It is necessary to cross tube 5 over tube 7 and tube 4 over tube 2 as shown in Figure 4.

      Notice: Lack of lubrication will make installation of the Upper Intake Manifold plenum difficult and may cause damage to the O-ring.

    8. Lubricate the Fuel Meter Body Upper Manifold O-ring (blue in color) with clean engine oil.
    9. Inspect Upper Intake Manifold Gasket and replace if necessary. Reinstall the Upper Intake Manifold plenum following the procedures in the Service Manual.

      Important: Lubricate the Fuel Inlet and Return Lines with clean engine oil before inserting them in the of the Fuel Meter Body.

      Make sure that Fuel Line Retaining Bracket is properly oriented with the tabs down.

       

       

    10. Cleaning Procedure Parts

      Part Number

      Description

      12345382

      Threadlock

      (NNN) NNN-NNNN/p>

      Top Engine Cleaner (U.S.)

      992872

      Top Engine Cleaner (Canada)

      12345104

      Port Fuel Injector Cleaner (U.S.)

      10953467

      Port Fuel Injector Cleaner (Canada)

      CSFI to MFI Conversion Parts

      Part Number

      Description

      12568332

      V-6 MFI Assembly

      88894355

      V-6 Bracket

      17113215

      V-6 Seal Kit

      93441235

      V-8 MFI Assembly

      17113206

      V-8 Seal Kit

      93442096

      V-8 Bracket

      This procedure outlines the steps required to replace the existing Central SFI Fuel System with a new MFI (Multiport Flexible Injection) Fuel System. Be sure to use the appropriate year and model Service Manual for proper disassembly and re-assembly procedure(s).
Customer: replied 5 years ago.
You have got to be kidding....I'm just a DIY guy and don't have the equipment or knowledge to do the above....How about using some injector cleaner to do this?
Expert:  Ken replied 5 years ago.
I was trying to show you th steps you need to take. 1st take this ti a shop and have the injectors cleaned. Check the news paper and your local adds. Make sure they are pressure cleaning the injectors and not the intake system.If the cleaning does not work then step 2. 2nd have the computer scanned when it is cold to see which cylinder is miss firing. Then you have to decide if you want replace that one injector or up date the hole spider with the new design. Sorry, just trying to give you all the infromation I have. Ken
Expert:  Ken replied 5 years ago.
Let me know if you have any more questions! Please remember to click "Accepted" or I do not get compensated for helping you tonight. Thank You Ken
Customer: replied 5 years ago.
I didn't get a response from you guys related to the fuel pressure test that I did that you guys ask me to do!   So, at this point, I'm not sure if my problem is due to fuel pressure or dirty injectors??? Also, if you think it's dirty injectors, why should I not try to use a fuel additive to clean them first and then have them removed and cleaned if that doesn't help.
Expert:  Ken replied 5 years ago.

56 psi is in spec. You do not have any lean fuel trim codes stored in the computer. The information you provided tells me your fuel pump is ok. The deposits on the tip if the injectors need a strong chemical and high pressure to get those deposits off. You should not run that chemical thought the fuel pump and lines. It will damage the fuel pump. The gas tank cleaners are very mild and in my experience they will not help when they get as bad as yours are. You can try it if you want, it may need to try that 2 or 3 times.

Most of the people that come in our shops want it fixed right now and are not willing to wait and see if the tank additive works. let me know if you have more questions. Ken
Customer: replied 5 years ago.
Thanks Ken...so your suggestion for this vehicle problem is to clean the injectors...and I agree with that..I'm going to at least try the fuel additive once to see if the problem gets any better...but I'm also going to take your advice and have the injectors cleaned per your reccomendations as soon as possible. If this doesn't resolve the issue, how to I re-connect with you for futher test?
Expert:  Ken replied 5 years ago.
I know the bullitin is long but it has all the answers you need. I have been fighting sticking injectors for years. GM even extended the warranty for for the spider for 10 years or 200000 miles or trucks with YF5 opton code because of this problem. You are over the 10 years and you might want to go talk to the service manager and see if they will help you out. A injector balance test may show this sticking valve if it is stuck that morning. Just post another guestion and request me. I look over the post almost every day. Your truck needs to have the YF5 option code. Ken
Ken, ASE Certified Technician
Category: GM
Satisfied Customers: 754
Experience: GM & SATURN Factory Trained Technician, 25 Years Experience
Ken and 11 other GM Specialists are ready to help you
Expert:  Ken replied 5 years ago.
If you go to the dealer do not tell them about "Just Answer." Tell them you have a friend that works at a dealer. They tend not to like us helping you. Problems like yours are the hardest to fix, keep working at it. You will get it. Thank You Ken
Customer: replied 5 years ago.
Ken...I have had the injectors cleaned (Technician said they were unusually clean) and problem is still there. Another Mechanic suggested that the problem might be linked to the MAF sensor. I would like your opinion on that ideal. Thanks
Expert:  Ken replied 5 years ago.
It may be, one of the things we do when we think its a MAF sensor is disconect it and drive it. This makes the system run off the MAP sensor. Or find a friend with a 5.7L and swap MAF sensors, they used the same part # XXXXX years.Did they do a injector balance test? Ken
Customer: replied 5 years ago.
I have a 1997 chevy Silverado with a 5.7L engine..Would that work?   Also, how will the vehicle act with the MAF disconnected? The Mechanic said that the injectors were operating with limits.. I don't know if that means he did a Balance test or not..
Expert:  Ken replied 5 years ago.
I think so, look at the part #s on the sensors. They will be the same. When the MAF fails It then runs off the MAP sensor. The problem is the computer cant tell when a sensor is not reading right. Only when they fail badly and are way out of range. Map sensors do get dirty on the sensing wire. I have cleaned them with some carb cleaner and a Q tip. Try to swap them if the part #s are the same. Ken
Customer: replied 5 years ago.
OK...I'll swap them if they are the same. If not, I'll disconnect it and see what happens..I'll be back later..
Expert:  Ken replied 5 years ago.

I will talk with the other drivablity tec in my shop in the AM for you. I will let him read this and see if he has any input. They can be tough when they don't set codes. Ken

Expert:  Ken replied 5 years ago.

I talked with the other tech in the shop today and he also was thinking injector. He thought it would be good to drive this in the A.M with a scan tool hooked up and watch the misfire counter. That will tell you if it is just one cylinder or all. Let me know how the MAF sensor did. You also might want to clean the throttle body and plate with some carb cleaner and a rag. Rub the plate and bore until they are shinny. Hole your foot down on the gas until it starts and then let off. If you have deposits built up in throttle body, the motor may not be getting enough air on take off. The motor uses more fuel and air when cold. You may also want to hook up a fuel gage and see if the fuel pressure holds after you turn off the motor. The fuel pressure regulators are known for dripping fuel when they first start going out. Ken

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